Re: [Harp-L] Re: THE COMB DEBATE REVISITED: SPAH Test

[Frank Mangiapane <frank.mangiapane@xxxxxxxxx>]

*Vern, if what you are saying about cover plates is true , then could
the rhetoric about the design of the cover plates on the Manji M-20 ,in
essence the opened back and side holes, be more hype than help ?
*
On Thu, Jul 15, 2010 at 4:57 PM, Vern <jevern@xxxxxxx> wrote:

>
> On Jul 13, 2010, at 9:57 PM, JohnnieHarp wrote:
>
> > Coverplate design and mods is one that comes to mind given current
> > claims made by customizers and manufactures as to volume increases,
> > etc, resulting from different coverplate forms (Suzuki Manji for
> > instance) ... personally, I have my doubts in the validity of these
> > claims based on my experiences ...
>
> There are acoustic principles to support your skepticism and experience.
>
> Diffraction:
> Through openings of less than a wavelength, sound spreads equally in all
> directions along circular wave-fronts.  Think of a pebble tossed in a pond.
> Because it is much shorter than a wavelength, the shape of a harmonica cover
> will not affect the direction of the sound.
>
> Logarithmic human hearing:
> The human ear has a logarithmic response...and a good thing that is!  The
> same ear that can hear the buzzing of a mosquito or the wind whispering
> through the pines is not destroyed by a clap of thunder or the output of a
> loud harmonica amp.  However, it means that a few holes or a slight change
> in shape of a cover that affect the emanated sound energy by a small amount
> will be imperceptible.  Besides that, the covers are usually touched,
> enclosed,  and their possible effect negated by a hand-cup.
>
> Cover design might/could have very minor effects on harmonica sound level,
>  but in real-world situations, the differences will be imperceptible.  The
> function of covers is to keep your hands off of the reeds.
>
> The cover materials have no effect at all.  Siegfried Nahrun made brass
> CX12 covers that sounded no different from black plastic ones.  The notion
> that a shiny gold coating on CX12 covers will affect the sound is laughable.
>
> I have blocked off half of the cover opening of a diatonic with a slab of
> metal thicker than the cover without changing the reading on my sound-level
> meter.  This means that bending the cover to increase the opening is futile.
>
> Vern
>
>
>
>


-- 
Franko